基于V4L2的Webcam应用过程详解【附源码】(6)

3. libswscale: 用于picture格式/大小转换, 占用cpu挺高 :), 用起来很简单, 基本就是

sws = sws_getContext(....);

sws_scale(sws, ...)

4. libx264 压缩: 考虑主要用于互动, 所以使用 preset=fast, tune=zerolatency, 320x240, 10fps, 300kbps, jj实测延迟很低, 小于 100ms

使用的数据结构

struct Ctx
{
 x264_t *x264;
 x264_picture_t picture;
 x264_param_t param;
 void *output;  // 用于保存编码后的完整帧
 int output_bufsize, output_datasize;
 int64_t pts;   // 输入 pts
 int64_t (*get_pts)(struct Ctx *);
 int64_t info_pts, info_dts;
 int info_key_frame;
 int info_valid;
};

vc_open(...) 设置必要的参数, 打开编码器

void *vc_open (int width, int height)
{
 Ctx *ctx = new Ctx;
 // 设置编码属性
 //x264_param_default(&ctx->param);
 x264_param_default_preset(&ctx->param, "fast", "zerolatency");
 ctx->param.i_width = width;
 ctx->param.i_height = height;
 ctx->param.b_repeat_headers = 1;  // 重复SPS/PPS 放到关键帧前面
 ctx->param.b_cabac = 1;
 ctx->param.i_fps_num = 10;
 ctx->param.i_fps_den = 1;
 ctx->param.i_keyint_max = 30;
 ctx->param.i_keyint_min = 10;
 // rc
 ctx->param.rc.i_rc_method = X264_RC_CRF;
 ctx->param.rc.i_bitrate = 300;
 //ctx->param.rc.f_rate_tolerance = 0.1;
 //ctx->param.rc.i_vbv_max_bitrate = ctx->param.rc.i_bitrate * 1.3;
 //ctx->param.rc.f_rf_constant = 600;
 //ctx->param.rc.f_rf_constant_max = ctx->param.rc.f_rf_constant * 1.3;
#ifdef DEBUG
 ctx->param.i_log_level = X264_LOG_WARNING;
#else
 ctx->param.i_log_level = X264_LOG_NONE;
#endif // release
 ctx->x264 = x264_encoder_open(&ctx->param);
 if (!ctx->x264) {
  fprintf(stderr, "%s: x264_encoder_open err/n", __func__);
  delete ctx;
  return 0;
 }
 x264_picture_init(&ctx->picture);
 ctx->picture.img.i_csp = X264_CSP_I420;
 ctx->picture.img.i_plane = 3;
 ctx->output = malloc(128*1024);
 ctx->output_bufsize = 128*1024;
 ctx->output_datasize = 0;
 ctx->get_pts = first_pts;
 ctx->info_valid = 0;
 return ctx;
}